The present invention relates in general to composite sandwich structures, and in particular to a new and useful thermoformable composite construction in which a corrugated core is bonded to a linerboard with a thermoplastic on one side, and to a moldable foam on the other side. The invention also includes a method of constructing the composite.
Composite board sandwich structures with parallel liners and at least one corrugated paper medium have a wide variety of applications. Such elements may be used, for example, as light weight, interior linings for walls, floors and ceiling panels, as facings, trims and headliners of automotive vehicles and for other applications where heat insulation, sound insulation and absorption and/or dampening of mechanical vibration are required. See, for example, U.S. Pat. Nos. 4,150,186, 4,170,674, and 4,933,225. The corrugated paper core in such prior art structures are typically adhered to opposite covering linerboards with an adhesive agent.
U.S. Pat. No. 3,867,240 discloses a composite panel for the headliner and other trim in an automobile, which includes a layer of rigid resin foam core. The core is sandwiched between paper linerboards for protecting the core. No corrugated layer is provided in this composite structure.
As recognized in the above-identified patents, insulation from heat and sound is almost indispensable. This is particularly true in the rooms of buildings, the cabins of ships, the interiors of automobile and some furniture applications.
Both in buildings and automobiles, a predominant method is to line the exterior structure with some type of insulating member. These members are normally attached to walls, floors and ceilings of buildings and automobiles. In some cases, however, the surfaces are not flat. This necessitates the insulating material to be shaped to the shape of the structure to be insulated. In addition to insulation, noise absorption may become critical in many building and automobile applications. When noise abatement is not sufficient to prevent infiltration of all unwanted noise, then noise absorption is required in order to attenuate the unwanted noise that would penetrate into the insulated space. It is important to accomplish this in an inexpensive manner and with as low a specific gravity as possible. U.S. Pat. No. 4,184,905 describes a heat and sound insulator of curved corrugated paperboard and method of shaping the structure, but it does not address the noise absorption problem.
In addition, rigidity may be necessitated when the insulator for building purposes is self-supported and more importantly if the material is used as a structural membrane for the interior of an automobile.
Noise absorbent materials are known which utilize fiberglass and resinated cotton. The use of fiberglass reinforced foam is also known.
Noise absorbent materials made of fiberglass and resinated cotton (shoddy) are impregnated with phenolic resins which require high temperatures of 200.degree.-240.degree. C. in order for the resins to cure. This high temperature precludes the molding and laminating, in a single step, of heat sensitive covering materials such as foam, foam backed cloth or vinyl to the fiberglass and resinated cotton structure. These decorative materials tend to burn or scorch when subjected to high temperatures. It would be advantageous to use moldable or formable foam, however, since it is much lighter than both resinated cotton and fiberglass. Also moldable foams form at lower temperatures allowing the covering material to be laminated while the substrate is being molded in one step.
Moldable or formable foams, resinated cotton and fiberglass have an advantage over linerboard plus corrugated core structures which are illustrated in the above-identified patents, in that they permit a deep draw when molded. Paper products using corrugated cores usually permit an elongation in the cross direction of only 5% and in the machine direction of only 2.5%. Due to these restrictions, it is difficult to achieve deep draws and/or contours. As a solution, resinated cotton or fiberglass may be used as a covering. The molding temperature again becomes a problem however.
Another requirement, in particular for automotive headliners, is flexibility. Automobile manufacturing currently requires that headliner substrates be foldable in order to facilitate their installation and serviceability. The headliner, for example, must be folded so that it can be introduced through available openings in the automobile body, for placement of the headliner against the ceiling of the automobile. The headliner must also be bendable to service various components that may be attached to the back section of the headliner.
The currently available headliners which include corrugated or other shaped core layers, are not restored to their original shape once they are folded. A visible crease remains in the structure.